What is the genetic advantage for Asian to have a hidden eyelid?

Question

I ask because they say Africans noses is shaped that way for the heat and Eurpeans nose is shaped a way for the cold. So what is the advantage for asians to have a hidden eyelid, because they live in all types of climates. Thanks

Answer 1

No ones certain as to the advantage of the epicanthal fold. In the Out of Africa theory it is a feature of the San bushman and may have left Africa with humans, so it's not an Asian acquisition per say, but rather others lost it.  One theoretical purpose may be to reduce glare or sunlight, which would explain why it is common in original peoples of savannah and tundra regions.  The feature may have cross the land bridge with the first peoples of North America as it is evident in some Native American groups as well.  While Asians today live in all climates their deep ancestors followed a relatively northern route to get there.  

Answer 2

The Asian eyelid is simply a short eyelid attached to a curtain. This curtain is a layer of skin then a layer of subcultaneous fat and then muscle. When the eye is opened. the curtain is actually the skin you see just below the eyebrow extending down to the crease of the eyelid.The short eyelid sits over the eye and the eyelid and curtain form a crease that looks like an occipital eye(that's the kind of eye everywhere else in the world) . In colder climates, many will have a thicker layer of fat in the curtain and it sags over the eyelid. This is called an inner fold and it hides the eyelid.

Native American eyes are Asian eyelids that are modified to meet iceage conditions. They have a thicker eyebrow fat pad and a thicker layer of subcultaneous fat in the curtain that acts like insulation from the cold. Additionally, the curtain can remain folded and when the eye is closed resulting in a double insulated short eyelid. This is the usual configuration when Native Americans close their eye. When looking down though, the eyelid will start to come down unfolded.

Answer 3

I'm not too sure on my accuracy here, but I've read that this eyelid fold is a feature all infants have, primairly in the womb, but when the nose bridge begins to jut out, the fold disappears.  Asians noses do not jut out, so they keep the fold.  

Answer 4

Epicanthal folds are not just Asian features.  One of my anthropology professors (a Lakota) had a theory that it aided in seeing well in the wind and in blizzards and to keep dust out of the eye.

Answer 5

It would be to keep wind and dust from blowing into the eye and drying it out, or otherwise irritating it...

Answer 6

I don't think there is one...